System and method to provide lubrication for a plug-in hybrid

ABSTRACT

In hybrid electric vehicles having increased battery storage capacity and plug-in capability, electric-only operation of significant duration is available. To supplement lubrication for the electric and mechanical components provided in a fluid circuit by an engine-driven mechanical pump, an electric pump is provided in parallel to the mechanical pump. When the electric pump is operating, a diagnostic can be performed to determine system integrity. According to one embodiment, an actual quantity provide to the circuit is determined; an expected quantity is estimated; and a fault is determined when the actual and expected quantities differ by more than a predetermined amount. The fault may indicate a leak or plug in the fluid circuit or a failure of a component in the fluid circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 12/488,842filed Jun. 22, 2009, the disclosure of which is hereby incorporated inits entirety by reference herein.

TECHNICAL FIELD

The present development relates to supplying oil to lubricate and coolcomponents in a hybrid electric vehicle.

BACKGROUND

Typical hybrid electric vehicles (HEVs) in widespread use have a limitedbattery capacity; in such systems the vehicle operates on electric-onlyoperation for limited periods of time. The components requiringlubrication are supplied by a mechanical pump coupled to the internalcombustion engine. Thus, in electric-only operation, the mechanical pumpdoes not rotate and supplies no oil to components in the oil circuit. Ithas been found that the amount of oil in the components is sufficientfor such limited periods of electric-only operation. In such HEVs, theamount of electric-only operation is limited, though, by how long thecomponents can survive on the residual lubricant in the system.

To further reduce petroleum consumption in HEVs, manufacturers aredeveloping plug-in hybrid electric vehicles (PHEVs). The battery pack ona PHEV has a greater storage capacity and the PHEV is provided withcharging capability to charge the battery pack from an electrical gridso that the PHEV derives its power from both the electrical grid andpetroleum sources. The duration of electric-only operation in a PHEV issignificantly increased in comparison to HEVs with limited batterycapacity. The lubrication and cooling needs of power-generating andpower-transmitting components in the PHEV are not satisfied by themechanical pump driven by the internal combustion engine.

SUMMARY

According to an embodiment of the present disclosure, an electric pumpis fluidly coupled to the oil circuit in parallel with the mechanicalpump. When the electric pump is operating, a diagnostic can be performedby determining an actual pressure in the circuit and an expectedpressure. The fault is determined when the actual and expected pressuresdiffer by more than a predetermined amount. The fault may indicate aleak or plug in the fluid circuit or a failure of a component in thefluid circuit.

According to an alternative embodiment, the diagnostic is performed byestimating an actual flow rate, estimating an expected flow rate, anddetecting the fault when the actual flow rate differs from the expectedflow rate by more than a predetermined amount.

An advantage is that the electric pump can be used as a diagnostic todetect faults in the fluid circuit without providing additional sensorsto perform such a diagnostic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an exemplary configuration ofmechanical components in a hybrid electric vehicle;

FIG. 2 is a schematic representation of an exemplary configuration of afluid circuit for lubricating and cooling components in a hybridelectric vehicle;

FIG. 3 is a schematic representation of sensors and actuators coupled toa control unit as part of a hybrid electric vehicle;

FIGS. 4 and 5 represent flow charts of methods according to embodimentsof the present disclosure; and

FIG. 6 shows an example pulse width train to drive an AC motor and theresulting magnetic flux that the pulse width train induces.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

As those of ordinary skill in the art will understand, various featuresof the embodiments illustrated and described with reference to any oneof the Figures may be combined with features illustrated in one or moreother Figures to produce alternative embodiments that are not explicitlyillustrated or described. The combinations of features illustratedprovide representative embodiments for typical applications. However,various combinations and modifications of the features consistent withthe teachings of the present disclosure may be desired for particularapplications or implementations. Those of ordinary skill in the art mayrecognize similar applications or implementations whether or notexplicitly described or illustrated.

In FIG. 1, a schematic of one exemplary mechanical arrangement ofcomponents in a HEV is shown. HEV 10 has multiple propulsion sourcescapable of providing power at the wheels 12, including: an internalcombustion engine 14, a traction motor 16, and a generator motor 18.Internal combustion engine 14 is coupled to a transaxle 19 via a shaft20. Shaft 20 drives a mechanical oil pump 22 via gear 24 and pump gear26, gear 24 being coupled to shaft 20. Mechanical oil pump 22 pumps oilthrough a fluid circuit. The fluid circuit is discussed further inregards to FIG. 2. Mechanical oil pump 22 is driven by engine 14; thus,when engine 14 is not rotating, mechanical oil pump 22 is not pumpingoil. Engine 14 is also coupled to planetary gears 28 of transmission 30.Transmission 30 includes planetary gears 28 as well as sun gear 32 andring gear 34. A generator motor 18 is coupled to sun gear 32 by shaft38. Traction motor 16 is coupled by a shaft 40 and gear 42 to ring gear34 of transmission 30. Traction motor 16 is coupled to wheels 12 ofvehicle 10 via a reduction gear set 44 and 46 and a differential 48.

The HEV embodiment shown in FIG. 1 represents one non-limitingarrangement. Alternatively, the components of FIG. 1 are arrangeddifferently and/or the system is comprised of different components.

The components enclosed within the dotted line of FIG. 1 are housedwithin the transaxle 19, according to one embodiment. Alternatively, thecomponents shown residing within transaxle 19 may be contained in morethan one housing.

Referring to FIG. 2, a schematic of the lubricant flow system withintransaxle 19 is shown. Both the mechanical pump 22 and an electric pump51 pump lubricant through fluid circuit 50. Pumps 22 and 51 are arrangedin parallel.

Mechanical pump 22 has a pressure relief valve 52 to ensure that amaximum system design pressure is not exceeded in fluid circuit 50. Inthe branch of fluid circuit 50 having electric pump 51, there is also afilter 54 and a heat exchanger 56. In alternative embodiments, filter 54and heat exchanger 56 are placed in other parts of fluid circuit 50.Lubricant is provided to generator motor 18 and to transmission 30before being returned to sump 58. Parallel to the flow passing throughmotor 18 and transmission 30 is another branch to heat exchanger 60 andtraction motor 16, which also returns flow to sump 58. For schematicpurposes, sump 58 is shown as a particular container within transaxle19. However, sump 58 may comprise the lower portion of transaxle 19,forming an oil pan of sorts. An oil pickup 62 extending into sump 58supplies oil to the inlet of pumps 22 and 51.

In FIG. 2, lubricant is shown being provided under pressure to generatormotor 18, heat exchanger 60, traction motor 16, and transmission 30.Alternatively and/or additionally, an oil reservoir 64 is provided nearthe top of transaxle 19. Reservoir 64 provides drip lubrication totraction motor 16 and generator motor 18. Within transaxle 19, rotatingcomponents splash lubricant within the casing of transaxle 19 providingyet another way that lubricant is transported within transaxle 19. Thefluid circuit shown in FIG. 2 is one example of many alternativeconfigurations to provide drip lubrication, pressurized lubrication,spray lubrication, and any combination thereof to the various componentswithin transaxle 19. Furthermore, the components in FIG. 2 may bearranged in a different order in the fluid circuit in an alternativeembodiment.

There are four modes of operation:

Mechanical Electric Mode pump 22 pump 51 Operating condition 1 On OnEngine 14 on; flow from mechanical pump 22 insufficient; supplement withelectric pump 51 2 On Off Engine 14 on; sufficient flow provided bymechanical pump 22 3 Off On Engine 14 off; use electric pump 51 to cooland/or lubricate system components 4 Off Off Engine 14 off; duration ofpure electric operation is short; residual oil from prior operation issufficient to cool and lubricate

In a HEV, whether the internal combustion engine 14 is operating isbased on many factors: state of charge of vehicle batteries, driverdemand, operating condition, and ambient conditions to name a few.Turning on engine 14 simply for driving mechanical oil pump 22 canconstrain HEV operation and negatively impact overall fuel efficiency ofthe operation, which is one of the disadvantages of the prior artovercome by an embodiment of the present disclosure in which electricpump 51 is provided in parallel with mechanical pump 22.

The terms oil and lubricant have been used interchangeably to describethe fluid within transaxle 19. In one embodiment the fluid is atransmission fluid. Alternatively, the fluid is any fluid that canlubricate the gears, motor bearings, and shaft bearings as well as carryenergy to the heat exchanger to keep the components housed withintransaxle 19 sufficiently cool and lubricated. In particular, tractionmotor 16 and generator motor 18 have two such demands: lubrication oftheir bearings and cooling of motor windings. Lubricant is also providedto transmission 30 to lubricate both gears and bearings. At a particularvehicle operating condition, cooling of traction motor 16 might be moredemanding than any other component in transaxle 19. At another operatingcondition, providing lubricant flow to transmission 30 may be mostdemanding. At even another operating condition, providing lubrication totraction motor 16 bearings may be most demanding. According to an aspectof the present disclosure, the amount of lubricant provided is dictatedby the most demanding component at any given operating condition.

A schematic representation of electrical connections for a HEV relevantto the present discussion is shown in FIG. 3. Power module 66 provides adriving current to electric pump 51. The control for the driving currentis commanded to power module 66 from an electronic control unit (ECU)68. Generator motor 18 and traction motor 16 may be provided currentfrom or provide current to power module 66 depending on the operatingmode of the HEV system. Power module 66 is coupled to a battery pack(not shown) as an electrical energy source/sink. Electric pump 51includes a pump driven by an electric motor. In one embodiment, theelectric motor is an AC motor, in which case the speed of the motor, andthus the pump, can be inferred, as will be discussed in more detailbelow. In another embodiment, the electric motor is a DC motor. In sucha situation, the electric pump speed can be measured by a speed sensor74 with the signal from speed sensor 74 provided to ECU 68. Speed sensormay be a Hall effect sensor proximate a toothed wheel rotating withelectric pump 51 or any other speed sensor known to one skilled in theart.

According to an embodiment of the present disclosure, operatingparameters associated with electric pump 51 can be used to infer flowrate and pressure in the fluid circuit. Such inferred values can bedetermined whether mechanical pump 22 is operated or not. When bothelectric pump 51 and mechanical pump 22 are operated, the flow rateprovided by mechanical pump 22 is estimated. Because mechanical pump 22is a positive displacement pump, its estimated output flow rate is basedon its rotational speed. Mechanical pump 22 is driven by and coupled toengine 14 via a gear set 24 and 26. Typically, engine 14 is providedwith a toothed wheel 70 and a Hall effect sensor 72. Sensor 72 providesa signal to ECU 68, from which engine speed is computed and mechanicalpump speed can be computed based on engine speed and a gear ratio ofgears 24 and 26.

Electric pump 51, in one embodiment, is driven by an AC motor. The pumpis controlled by applying a pulse width modulated signal, such as 80shown in FIG. 4. The frequency, reciprocal of period, and width of thepulse train 80 applied to windings of an AC motor induces a magneticflux due to a resulting current flow 82, thereby causing the AC motor torotate. The rotational speed of the AC motor is based on the timing andpattern of the applied pulses. The pulses applied to the windings are oflonger duration and resulting AC current is higher when a load on the ACmotor is high. In such a manner, the torque of the motor can beinferred, or estimated, based on the resulting AC current.

A flowchart showing an embodiment of the present disclosure to determinethe component having the most demanding lubrication requirement is shownin FIG. 5. The algorithm starts in 100 and passes control to block 102to determine whether the key is on. If not, control passes to block 102until a positive result is encountered. Upon a positive result in 102,control passes to block 104 in which a temperature of the windings in afirst electric motor, Tw1, a temperature of the windings in a secondelectric motor, Tw2, and a powertrain component volumetric flow rate, V,are determined. These three quantities are provided by way of exampleand not intended to be limiting. For example, in another embodiment, adetermination of sufficient lubrication can be based on pressure inplace of flow rate. In yet another alternative, the flowchart in FIG. 4can be contracted or expanded to include fewer or more decision blocks,examples include: three desired pressures (as demanded by a generatormotor, a traction motor, and a transmission); two desired maximumtemperatures (traction motor and generator motor) and one minimum flowrate (through transmission) and one maximum temperature (tractionmotor).

Motor winding temperature set points, Tsp1 and Tsp2, may be based ontotal transaxle 19 losses, preferred motor winding operatingtemperatures or other criteria. The volumetric flow rate set point, Vsp,may be based on transaxle 19 losses, wear tables, or other criteria. Inblocks 106, 108, and 110, it is determined whether Tw1 is greater than afirst set point temperature, Tsp1, whether Tw2 is greater than a secondtemperature set point, Tsp2, and whether the volumetric flow rate, V, isless than a volumetric flow rate set point, Vsp, respectively. If anyone of these conditions returns a positive result indicatinginsufficient lubricant flow, control is passed to block 112 in which thefrequency of the AC current is increased to increase the pump rotationalspeed. In another alternative, the pump is driven by a DC motor andpulse width to the motor is increased to increase motor rotationalspeed. Or, in another alternative, the speed of electric pump 51 isincreased in block 112 according to any other known manner, such ashaving multiple, selectable windings in electric pump 51, which can beswitched in and out to affect pump capacity. If negative results arereturned in all of blocks 106, 108, and 110, control passes to block 114in which it is determined whether temperatures, Tw1 and Tw2, are lowerthan their respective set point temperatures, Tsp1 and Tsp2, by morethan suitable safety factors, Tsf1 and Tsf2, respectively. It is alsodetermined whether the volumetric flow rate exceeds the volumetric flowset point by a suitable safety factor, Vsf. The expressions in block 114are evaluated using a Boolean “and” operation. Thus, control passes toblock 116 only if all the expressions are true; otherwise, controlpasses to block 104. A positive result from block 114 passes control toblock 116 in which it is determined whether electric pump 51 is on. Ifit is not, no further decrease is possible and control passes to block104. If the electric pump is on, control passes to block 118 in whichspeed of electric pump 51 is decreased with control returning to block104. Depending on the type of electric motor coupled to the pump, thespeed is decreased by decreasing the AC frequency, the pulse width, etc.

Continuing to refer to FIG. 5, when speed of electric pump 51 isincreased in 112, control passes to 120 in which is determined whetherthe pump speed is greater than or equal to the maximum pump speed. Ifnot, control passes to 104. If so, control passes to 122 to notify theECU of the over speed condition. Also in 122, electric pump speed is setto the maximum speed before returning to block 104.

In other embodiments, a time rate of change quantity is also compared toa threshold to determine whether additional fluid supply is desired. Forexample, an electric motor that is converting electrical energy intomechanical energy or vice versa can heat up very quickly. Thus, adesired cooling level can be based on both the temperature of thewindings as well as a rate of change of the temperature of the windings.Additional refinements, such as use of a PID controller, are obvious toone skilled in the art.

In FIG. 5, safety factors, Tsf1, Tsf2, and Vsf, are employed. Inalternative embodiments, the safety factors are set to zero. Also inFIG. 5, first and second temperature maxima, Tmax1 and Tmax 2, areshown. In one embodiment, the same maximum temperature is used to detectoverheating in both electric motors with Tmax1 equal to Tmax2.

It is desirable to maintain the temperature in generator motor 18 andtraction motor 16 below a temperature at which damage can result ormaximum operating temperature. The temperature in the motor can beestimated based on a model of energy generation within the motor as wellas the energy rejection to the lubricant based on flow to and heattransfer characteristics of the motor. Alternatively, motor temperaturecan be estimated based on a signal from a sensor in or near the motor.In yet another alternative, the temperature is estimated from a measureof resistance of the windings:

R=Rref [1+α(T−Tref)]

where Rref is the resistance at reference temperature, Tref, and α isthe change in resistance per degree temperature change, a materialproperty. Solving for T:

T=Tref+(1/α) (R/Rref−1).

As discussed in regards to FIG. 5, control is based on estimatingtemperature of the motor windings. Alternatively, control could be basedon maintaining the resistance in the windings below a threshold. In yetanother alternative, a flow rate can be determined which provides thedesired cooling. Control can be based on providing that flow rate.

Referring to FIG. 6, a diagnostic routine starts in block 150. In 152,it is determined whether electric pump 51 is operating. If it is not,pump 51 is turned on in 154 prior to proceeding to 156 in which thespeed and torque of electric pump 51 are determined. In 158 the speed ofmechanical pump 22 is determined. Blocks 156 and 158 can be performed inany order. Control passes to block 160, in which the total flow rate isdetermined. Control passes to block 162 in which actual electric pumpoutput pressure is determine based on torque. Control then passes toblock 164 in which expected pressure is determined based on flow rateand fluid temperature. Block 164 can be a lookup table or computationbased on, e.g., a polynomial equation. Block 166 provides inputinformation for the computation or table lookup in block 164, providingat least the fluid viscosity as a function of temperature and the losscharacteristics of the fluid circuit. Control passes to decision 168 todetermine whether the absolute value of the difference in the actual andexpected pressures exceeds a predetermined pressure difference. Apositive result in decision 168 indicates that a fault is detected andcontrol passes to block 170 in which the fault is indicated by setting afault code or a light indicating a fault to the operator of the vehicle.Alternatively, specific high and low limits may be set based upontypical failure modes. Otherwise, control passes to block 172. Ratherthan run a diagnostic test continuously, in one embodiment, block 172inserts a delay. In an alternative embodiment, the diagnostic isexecuted only when electric pump 51 is operating, i.e., the pump isn'tturned on simply for diagnostic purposes.

While the best mode has been described in detail with respect toparticular embodiments, those familiar with the art will recognizevarious alternative designs and embodiments within the scope of thefollowing claims. While various embodiments may have been described asproviding advantages or being preferred over other embodiments withrespect to one or more desired characteristics, as one skilled in theart is aware, one or more characteristics may be compromised to achievedesired system attributes, which depend on the specific application andimplementation. These attributes include, but are not limited to: cost,strength, durability, life cycle cost, marketability, appearance,packaging, size, serviceability, weight, manufacturability, ease ofassembly, etc. The embodiments described herein that are characterizedas less desirable than other embodiments or prior art implementationswith respect to one or more characteristics are not outside the scope ofthe disclosure and may be desirable for particular applications.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A fluid circuit, comprising: an electric motor; atransmission; a mechanical pump arranged in the fluid circuit with theelectric motor and the transmission, the mechanical pump adapted tocirculate fluid to provide cooling and lubrication to the transmissionand electric motor; an electric pump arranged in the fluid circuit inparallel with the mechanical pump; power electronics electricallycoupled to the electric pump to control a speed and a torque of theelectric pump; and an electronic control unit electronically coupled tothe power electronics to estimate pressure and flow rate.
 2. The fluidcircuit of claim 1 wherein: the electric pump is an AC electric pump;the power electronics comprises an inverter; and the electronic controlunit estimates the flow rate based on the speed of the electric pump andthe pressure based on the current supplied to the electric pump.
 3. Thefluid circuit of claim 1 wherein: the electric pump is a DC electricpump; the power electronics provides a pulse width modulated pulse trainto the electric pump; and the electronic control unit estimates the flowrate based on the speed of the electric pump and the pressure based onthe current supplied to the electric pump.
 4. The fluid circuit of claim3, further comprising: a speed sensor proximate the electric pump andelectronically coupled to the electronic control unit wherein the speedof the electric pump is based on a signal from the speed sensor.
 5. Amethod to determine a fault in a fluid circuit fluidly coupled with atleast an electric motor and transmission, comprising: estimating a flowrate provided by an electric pump disposed in the fluid circuit;determining an expected pressure based on the flow rate; estimating anactual pressure based on a load on the electric pump; and detecting thefault when the actual pressure differs from the expected pressure bymore than a predetermined amount.
 6. The method of claim 5 wherein: theelectric pump is an AC pump; the actual flow rate is based on a speed ofthe electric pump; and the speed is based on an AC drive frequencysupplied to the electric pump.
 7. The method of claim 5 wherein theexpected flow rate is further based on temperature of the fluid.
 8. Themethod of claim 6 wherein: a mechanical pump is also fluidly coupledwith the fluid circuit; the mechanical pump is arranged in parallel withthe electric pump; and the actual flow rate is further based on a speedof the mechanical pump.